1. Field of the Invention
The present invention relates to an electric transaxle including an axle, an electric motor for driving the axle, a gear mechanism for transmitting power front the electric motor to the axle, and a transaxle casing incorporating the gear mechanism.
2. Related Art
Conventionally, as disclosed by JP H09-226394 A, there is a well-known electric transaxle including an axle, an electric motor for driving the axle, a gear mechanism for transmitting power from the electric motor to the axle, and a transaxle casing incorporating the gear mechanism. The transaxle casing defines a gear chamber incorporating the gear mechanism, and fluid for lubricating the gear mechanism is accumulated in a bottom portion of the gear chamber so as to serve as a fluid sump (hereinafter, referred to as “first fluid sump”), and the gear mechanism is submerged in the first fluid sump. Further, the transaxle casing is provided in an upper portion with another fluid sump (hereinafter referred to as “second fluid sump”) supplied with fluid that is raised and splashed from the first fluid sump by rotating gears of the gear mechanism. The electric motor is externally mounted on the transaxle casing so as to define a motor chamber incorporating component elements of the electric motor, such as a stator and a rotor, and fluid is supplied from the second fluid sump into the motor chamber so as to cool the electric motor.
In the above-mentioned conventional electric transaxle, the motor chamber is used as a third fluid sump for adjusting a level of the first fluid sump in height by supply or discharge of fluid to and from the motor chamber. In this regard, when the vehicle is stationary, the gears are not rotated to raise and splash fluid of the first fluid sump, whereby the level of the first fluid sump has a sufficient height so that the gear mechanism is sufficiently submerged in the first fluid sump so as to be ready for starting the vehicle. On the other hand, during travel of the vehicle, fluid of the first fluid sump is raised and splashed by rotating the gears and is stored in the second fluid sump of the transaxle casing and in the third fluid sump of the motor chamber, thereby lowering the level of the first fluid sump, and reducing resistance of the first fluid sump to stirring of the gears. Accordingly, the submergence depth of the gear mechanism in the first fluid sump is reduced, however, the rotating gears stir the first fluid sump so as to supply fluid from the first fluid sump to all the corners of the gear mechanism, thereby ensuring sufficient lubrication of the gear mechanism.
The transaxle casing is formed with a structure for smoothly guiding the fluid raised and splashed from the first fluid sump to the second fluid sump. However, this structure is available for only guiding fluid splashed by the gears rotating in one direction for forward traveling of the vehicle. The structure is not configured to ensure smooth introduction of fluid from the first fluid sump to the second fluid sump when the gears rotate in the other direction for backward traveling of the vehicle, because the electric transaxle is designed to be adapted to ordinary motorcars that do not often travel backward. If the electric transaxle is adapted to a working vehicle that often reverses its traveling direction, fluid raised and splashed by the gears rotating in the direction for backward traveling of the vehicle is insufficiently supplied to the second fluid sump, thereby insufficiently lowering the level of the first fluid sump for reducing resistance of the first fluid sump to stirring of the gears, and thereby insufficiently supplying the motor chamber with fluid for cooling the electric motor from the second fluid sump.
Further, in the above-mentioned conventional electric transaxle, the fluid passage for supplying fluid from the second fluid sump to the motor chamber includes a portion defined by the electric motor, however, this portion includes a fluid passage formed in a motor shaft serving as an output shaft of the electric motor, thereby being complicated, increasing costs, and deteriorating maintenanceability.
Further, the above-mentioned conventional electric transaxle is limitative in arrangement because the mounting direction of the electric motor and the arrangement of the first and second fluid sumps are limitative. Therefore, if a different arrangement of the electric motor relative to the transaxle casing or relative to the axles is desired, an additional different die or member must be prepared, thereby increasing costs. Furthermore, the electric transaxle is desired to reduce costs because it must have an expensive electric motor.